penance

Short definition from Wiktionary

Noun

1. 1
   A voluntary self-imposed punishment for a sinful act or wrongdoing. It may be intended to serve as reparation for the act.
2. 2
   A sacrament in some Christian churches that involves penitence (remorse plus restitution via prayer).
3. 3
   Any instrument of self-punishment.
4. 4
   repentance
5. 5
   pain; sorrow; suffering

Verb

1. 1
   To impose penance; to punish.